Many in the field who use virtual data storage subsystems use it for the copying of logical files or volumes. Virtual refers to a functional unit that appears to be real to a host processor but where the functions are accomplished by other means. Virtual storage involves storage space that may be regarded as addressable main storage by the host processor in which virtual addresses are mapped into real addresses. The amount of virtual addresses are finite, and a host processor must first search for virtual addresses which have been flagged as available whenever it wishes to store data.
A virtual subsystem can be implemented using a Direct Access Storage Device (DASD) subsystem. The DASD subsystem allows the user to define a maximum number of a plurality (typically 256) of virtual functional devices. Each device is defined with a certain finite size, i.e., a certain number of addressable tracks. A track is a unit of space on a disk at which data can be stored. A logical file or volume is stored in a plurality of tracks. The user, either through the host processor or the DASD control panel, defines the devices on a disk to be used by the subsystem. Copies of tracks are often made to the devices for migration to permanent backup media either in parallel or at a later time. Under an existing process commonly referred to as "SnapShot", data may only be copied either within a device or from one device to another within the subsystem. SnapShot's underlying structure is disclosed in Belsan et al., U.S. Pat. No. 5,410,667, filed Apr. 17, 1992, and is fully incorporated by reference herein. Thus, the amount of addressable space on the disk available for an execution of a copying task is limited by the size, i.e., the number of tracks, of a device. This limits the subsystem's ability to copy data.
There is a need to provide additional addressable functional space on a disk for use by the host processor using a virtual data storage subsystem. The additional addressable functional space will alleviate the host processor from having to conduct a search for available space within any device whenever space on the devices become scarce. This method and system should be cost effective, easy to implement, easily adaptable, and host processor independent. The present invention addresses this need.